1. Field of the Invention
This invention relates generally to sound signal generators and more particularly is directed towards a new and improved gas-actuated sound signal generator that is particularly useful in connection with tire pressure sensing systems.
2. Description of the Prior Art
It is known that the pressure of a pneumatic tire may be monitored for either low or high pressure conditions by means of a device mounted to the wheel and adapted to generate a sound signal upon the occurrence of a high or low pressure event. The sound signal is then detected by a transducer forming part of a processing system for actuating an alarm device to alert the driver of the vehicle. By way of example, U.S. Pat. Nos. 3,489,998; 3,738,308; 3,890,595 and 3,934,223 show systems of this type. Also in co-pending application Ser. No. 665,889, filed by William A. Barabino Mar. 11, 1976, entitled "Method and Apparatus for Monitoring Tire Pressure," and assigned to the same assignee as the present application, there is disclosed a system of the same general sort in which the system is protected against actuation by false signals from background noise rather than true signals from the wheel mounted devices. In the co-pending application, this protection is achieved by the use of coded signals produced by two discrete frequencies generated by the wheel mounted device, resulting in amplitude modulation of the carrier with the signal being detected and decoded through processing circuitry.
In prior art devices, the sound signal generators have presented production difficulties from the standpoint of reproducibility, variation in performance, time needed to adjust individual devices and other factors.
Accordingly, it is an object of the present invention to provide a simple, low-cost sound signal generator which is easy to fabricate and assemble, requires no adjustment and provides inherently repeatable performance. Another object of this invention is to provide a highly efficient sound signal generator of highly stable performance and one which may be fabricated to emit multiple discrete frequencies for coding purposes.